in your (excellent) bibliography, you list OP 1915 as having three impressions (1915, 2 in 1916), each indicated on the label of the front cover.

This eBay auction is a 1930 impression (also notes a 1924 impression) with a label on the front cover that does not seem to indicate any impressions.

The photos are poor (not quite "worst" caliber since I can read most of what I need to) but it seems an accurate listing. Were they printing this book into 1930? Time to check the impression page and not just look at those front cover labels...